We have immunopurified CENPA containing chromatin complexes from normal (HeLa) and 4 colorectal cancer cell lines. We find that there appear to be two fractions of CENPA in the genome and that CENPC may be differentially localized in these two fractions. Experiments are currently underway to precisely pinpoint using atomic force microscopy how CENPC is bound to CENPA. We have created multiple CENPA constructs with "swapped" domains to further dissect precisely which part of the CENPA protein is essential for direct or indirect interaction with the CENPC and other core kinetochore proteins in human cells.